How Much Rain Did LA Get This Week? Enough To Put Us On Track For A Normal Year

The Hollywood sign during a rain storm in 2017. (AFP/Getty Images)

This week's rain drenched the Los Angeles Basin, showering Manhattan Beach and USC with an inch, and dumping four inches at Clear Creek.

Storms caused chaos on the roads and the cancellation of at least one Hollywood meeting, but we at LAist wanted to know how much rain the region really got.

The answer: seven percent of a normal year's accumulation.

The seven percent figure — basically the jump in the blue line over the last couple days — comes courtesy of David Pierce at the Scripps Institution of Oceanography. At KPCC/LAist's request, Pierce devised a metric that captures the rainfall picture across Southern California.

He does that by factoring in rainfall totals from 20 weather stations. They span SoCal, including coastal areas from Newport Beach to Santa Barbara, and inland regions including Redlands and Mount Wilson. He weights them according to geography and historical weather data.

Another feature Pierce sought out was a detailed historical record. Many of these stations have operated since World War II.

"The whole purpose of this was to try to come up with a single number that really is capturing how wet, or dry, the region really is," Pierce told KPCC in 2016.

The cool thing about this metric is that it updates as data flows in from gauges. Right now, it shows that the showers brought us to a 'water year' total of nearly thirteen percent.

What's a water year? It's the period between October and September that scientists use to track precipitation in the West.

The 12.7 percent you see is very close to the historical median for November 30, which is 13.3 percent. You can track the median by the light gray line on the chart above.

This time of year — which, before the effects of climate change started accelerating, was fairly reliably rainy — that line only gets steeper. To keep pace with the median year, we'll need many more storms like the one we saw this week.

And ... we could use them. Most of L.A. County remains in a severe drought, according to the U.S. Drought Monitor. Parts of coastal L.A., Ventura and Santa Barbara counties remain in extreme drought.

The outlook for the rest of the winter isn't great, either. The National Oceanic and Atmospheric Administration said in October that drought conditions are likely to continue over a hot, dry winter.


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